DE 101 39 142 A1 describes an exhaust gas treatment device of a combustion engine, which uses a SCR-catalyst (selective-catalytic-reduction) for the reduction of the NOx-emissions that reduces the nitrous gases that are in the exhaust gas with the reducing agent ammoniac into nitrogen. The ammoniac is won in the exhaust gas area of the combustion engine from a urea/water solution that is sprayed into the exhaust gas area upstream before the SCR-catalyst. The urea/water solution that is stored in a storage tank is brought to a default metering pressure by a pump. For dosing the urea/water solution depending on the demand a metering valve is provided, which is adjusted to a default flow.
DE 10 2004 044 506 A1 describes a procedure and a device at which a reagent that is also under pressure is sprayed into the exhaust gas of a combustion engine before a SCR-catalyst. To support the spray process the familiar system uses compressed air that is led over a check valve, which provides an opening pressure. A diagnosis of the compressed air pressure is provided, which begins at a starting point of time of the diagnosis with the closing of the compressed air regulating valve. It is checked at least at a second point of time, whether the compressed air pressure corresponds with at least one lower threshold value, which corresponds at least approximately with opening pressure of the check valve that has been added to the ambient air pressure. An error-signal is provided if the condition is not fulfilled.
DE 10 2005 001 119 A1 describes a procedure and a device, which provides the spraying of an oxidizable reagent in the form of fuel into the exhaust gas area of a combustion engine upstream before an exhaust gas treatment device, which for 0065 ample contains an oxidation-catalyst, a particle filter, a NOx-storage catalyst and/or a SCR-catalyst, whereby the exhaust gas treatment device or at least a part of it shall be heated. A diagnosis of the exhaust gas treatment device is provided by controlling the reagent pressure. The reagent pressure that has been measured between a reagent security valve and a reagent metering valve is determined during different statutes of the reagent security valve and/or the reagent metering valve and compared with at least one threshold value. An error signal is provided in the case of a threshold exceeding.
DE 10 2004 043 366 A1 describes a procedure and a device, which again provides the spraying of a urea/water solution as the reagent that is under pressure into the exhaust gas of a combustion engine upstream before a SCR-catalyst. The familiar system provides a support of the spraying process by compressed air. the urea/water solution that is under pressure is led over a spray pip into the exhaust gas area of the combustion engine. A diagnosis is provided, at which it is checked, whether the spray pipe is completely or at least partially blocked. The diagnosis is started at a starting point of time by reducing the reagent pressure as well as the compressed air pressure. The time course of the reagent pressure that is detected after the starting point of time is checked, upon whether a reagent pressure drop occurred. Also the time course of the compressed air pressure that is detected after the starting point of time is checked, upon whether a compressed air pressure drop occurred. An error signal is provided, when each the reagent pressure and the compressed air pressure drop do not fall below a threshold value.
DE 10 2004 022 115 A1 again describes a procedure and a device, which provide the spraying of a urea/water solution as reagent that is under pressure into the exhaust gas of a combustion engine upstream before a SCR-catalyst. Also this familiar system uses compressed air to support the spraying process. A diagnosis of at least one pressure sensor is implemented, whereby a pressure sensor can be arranged in the reagent path as well as in the compressed air path. In at least a first time interval, in which a stationary pressure status should occur, it is checked, whether the pressure signal corresponds at least approximately with a default check pressure and/or whether a default change towards the stationary pressure occurred at least approximately. An error signal is provided, if at least one condition is not fulfilled.
The invention is based on the task to provide a procedure for diagnosing a metering valve of an exhaust gas treatment device and a device for implementing the procedure, which deliver a reliable diagnosis result.
The task is solved by the measures that are stated in the independent claims.